Optical access disconnection systems and methods

ABSTRACT

An access disconnection system includes: a material capable of absorbing blood from a patient upon an arterial or venous line disconnection; a light emitter positioned to emit light onto the material; a light receiver positioned to receive light reflected off of the material; and electronic circuitry operably coupled to at least one of the light emitter and receiver, the circuitry configured to provide an output (i) when light received by the receiver reaches a particular level or (ii) indicative of an amount of light received by the light receiver.

BACKGROUND

The present disclosure relates generally to patient access disconnectionsystems and methods for medical treatments. More specifically, thepresent disclosure relates to the detection of a patient accessdisconnection, such as the detection of needle or catheter dislodgmentduring dialysis therapy.

FIG. 1 illustrates a known access disconnection configuration. Blood isdrawn from an arm 12 of a patient through an arterial line 14 connectedthe patient via an arterial needle 16. Blood is returned to the patient,after it has been treated, via a venous line 18 and venous needle 20.Needles 16 and 20 actually connect to a shunt 22, which is placed influid communication with one of the patient's arteries and veins.Accidental disconnection of the arterial line 14 during treatment is notas serious an issue as this simply eliminates the source of blood to theblood pump. Access disconnection of venous line 18 during treatment is aserious concern because arterial line 14 keeps feeding blood to theblood pump, while venous line 18 returns blood to a location outside ofthe patient.

A variety of different medical treatments relate to the delivery offluid to, through and/or from a patient, such as the delivery of bloodbetween a patient and an extracorporeal system connected to the patientvia a needle or needles inserted within the patient. For example,plasmapherisis, hemodialysis, hemofiltration and hemodiafiltration areall treatments that remove waste, toxins and excess water directly fromthe patient's blood. During these treatments, the patient is connectedto an extracorporeal circuit and machine, and the patient's blood ispumped through the circuit and machine. Waste, toxins and excess waterare removed from the patient's blood, and the blood is infused back intothe patient.

In these treatments, needles or similar access devices are inserted intothe patient's vascular system so that the patient's blood can betransported to and from the extracorporeal machine. Traditionalhemodialysis, hemofiltration and hemodiafiltration treatments can lastseveral hours and are generally performed in a treatment center aboutthree to four times per week. In in-center treatments, patientsundergoing hemodialysis, for example, are monitored visually to detectneedle dislodgment. However, the needle may not be in plain view of thepatient or medical staff (e.g., it may be covered by a blanket) suchthat it could delay detection and timely response.

Moreover, in view of the increased quality of life, observed reductionsin both morbidity and mortality and lower costs with respect toin-center treatments, a renewed interest has arisen for self-care andhome therapies, such as home hemodialysis. Such home therapies (whetherhemodialysis, hemofiltration or hemodiafiltration) can be done duringthe day, evening or nocturnally. If unsupervised or asleep, dislodgmentrisks increase because a caregiver is not present and perhaps even thepatient is not aware of a dislodgment.

Various systems exist for detecting needle dislodgement in hemodialysis.For example, U.S. Pat. No. 7,022,098 (“the '098 Patent”) and U.S. Pat.No. 7,052,480 (“the '480 Patent”), both entitled Access DisconnectionSystems And Methods, and assigned to the eventual assignee of thepresent application, disclose access disconnection systems that measurean electrical impedance of the extracorporeal dialysis circuit connectedto the vascular access needles. An external voltage or current source isused to inject a small current (e.g., less that 2.5 μ-Amp) into theblood flow. While this external current is small compared to othersystems, the source still requires that measures be taken to ensure thatthe current does not exceed 10 μ-Amp, which is considered in the art tobe a safety limit for intercardiac devices. Further, sensitivity of theimpedance system can be decreased when the patient is connected to earthground (e.g., through grounding devices found in clinics and homes).

Another problem with systems that inject current into the extracorporealcircuits occurs if the dislodged needle reestablishes contact with theother needle through leaked blood. Here, the electrical parameter beingsensed, e.g., impedance, may not change or not change enough to signalan access disconnection even though one has occurred.

A further obstacle involves the addition of contacts to the disposableportion of the blood treatment system. Metal or otherwise conductivemembers placed in the disposable add a certain amount of manufacturingdifficulty and cost.

A need accordingly exists for improved blood access disconnectionsystems.

SUMMARY

The examples described herein disclose access disconnection systems andmethods applicable for example to: plasmapherisis, hemodialysis (“HD”),hemofiltration (“HF”) and hemodiafiltration (“HDF”). The accessdisconnection systems may also be used with continuous renal replacementtherapy (“CRRT”) treatments requiring vascular access. The accessdisconnection examples below operate with systems having a diffusionmembrane or filter, such as a dialyzer, e.g., for HD or HDF, or ahemofiliter, e.g., for HF.

Moreover, each of the systems described herein may be used with clinicalor home setting machines. For example, the systems may be employed in anin-center HD, HF or HDF machine, which runs virtually continuouslythroughout the day. Alternatively, the systems may be used in a home HD,HF or HDF machine, which is run at the patient's convenience. One suchhome system is described in U.S. Pat. No. 8,029,454 (“the ′454 Patent”),entitled “High Convection Home Hemodialysis/Hemofiltration And SorbentSystem,” filed Nov. 4, 2004, assigned to the eventual assignee of thepresent patent, the entire contents of which are incorporated hereinexpressly by reference.

The access disconnection examples below operate with systems having adialysate (infusate) supply, which can be a single bag or multiple bagsof dialysate supply ganged together and used one after another. Furtheralternatively, each of the access disconnection systems shown below canbe used with a machine having an on-line source, such as one or moreconcentrate pump configured to combine one or more concentrate withwater to form dialysate on-line. On-line sources are used commonly withHD systems for example.

Various non-invasive access disconnection systems are described herein.The systems by and large do not inject a voltage or current into thepatient. This illuminates problems with patient grounding inherent incurrent inducing systems. Because the systems do not rely on theconnection or disconnection of an electrical loop, they tend to beimmune from the reestablishment of a conductive path with a dislodgedneedle and lost blood. The disclosed systems in various embodimentscommunicate with the dialysis machine wirelessly, e.g., through a radiofrequency signal. In this manner, the systems do not add to thedisposable tubing and/or cassette that the machine uses, increasingmanufacturing feasibility and reducing cost.

A first system uses a piezoelectric or electromagnetic transducer(referred to hereafter generally as piezoelectric for convenience)operating for example in the Mega-Hertz frequency range, which transmitsultrasound waves into tissue. The transducer's body is parallel to thetissue in one embodiment while the piezoelectric itself is at an angleto produce ultrasound components aligned with blood flow direction.

Red cells in the blood stream act as reflectors for the ultrasound,echoing the wave back into the transducer. Another piezoelectric orelectromagnetic crystal (referred to hereafter generally aspiezoelectric for convenience) can be used to receive the echoes.Ultrasound frequency is changed as the wave reflects on the blood cellsvia the Doppler effect. The changes in frequency of the ultrasoundsignal are an indication of the speed of the reflecting cells. The firstsystem processes the received echoes and extracts flow rate information.

The first system as mentioned uses a piezoelectric transmitter and apiezoelectric receiver or a single transducer that performs bothfunctions. Electronic circuitry is connected to the transducers ortransducer to produce the excitation signals and to process the echoes.In one implementation, the electronics also include a radio frequency(“RF”) link to the hemodialysis instrument. Once the treatment hasstarted, the ultrasound device gathers information from the bloodstream. Peak speed of reflectors, pulsatile characteristics of the bloodflow, turbulence in the access are some of the parameters that aremonitored as described in more detail below. The access disconnectionsystem exchanges such information with the dialysis instrument via theRF link. Venous needle dislodgement will necessarily introduce a radicalchange in the sensed parameters, allowing access disconnect detection.

In one implementation of the first access disconnection system, theultrasound transducer is held in place with a band via a hook and loopassembly, magnetic coupling or other buckle mechanism. The band offerstube restraining to mechanically prevent needle dislodgement.

A second access disconnection system uses the propagation properties ofsound in blood within the extracorporeal circuit to determine forexample if the venous section of the extracorporeal circuit is connectedto the patient. The second system uses at least one acoustic transducer,which generates a sound wave signal that is processed by the dialysisunit, which has access to other parameters of the treatment such asblood flow, dialysis flow, valve sequencing etc. The sound waves can besonic, subsonic or a pressure wave emitted into the blood stream. Thesignals can be of any suitable frequency, could be a single frequency ormultiple frequencies, it could be continuous, pulsed, modulated inamplitude, frequency or phase. The acoustic transducer can bepiezoelectric, electromagnetic or any suitable type capable ofconverting electrical excitation into pressure waves and/or vice versa.

The second access disconnection system can be implemented in at leastthree ways. One implementation uses two acoustic transducers, onecoupled to the venous section of the extracorporeal circuit, while theother is coupled to the arterial section of the extracorporeal circuit.One of the transducers transmits an acoustic signal into the bloodstream, while the other transducer receives the signal. If any of thesections becomes disconnected, the receiver no longer detects theemitted signal, triggering an alarm. The dual acoustic transducers caneach perform both functions, transmit and receive, making possible anembodiment in which the dual transducers switch functions with eachother.

A second implementation uses either one acoustic transducer, doubling astransmitter and receiver, or two transducers, one dedicated to transmitand the other to receive. Here, both emitter and receiver are coupled tothe venous section of the extracorporeal circuit. In this implementationthe transmitter sends an acoustic pulse into the blood. The pulsereflects in the extracorporeal circuit interface producing a signatureresponse. The system monitors, processes and analyzes the signature ofthe echo produced when the venous line is connected and yields abaseline acoustic signature response. The acoustic signature responseproduced when the venous line is disconnected is different from thestored pattern. Processing of the received signal detects such changeand generates an alarm, pump and/or valve shutdown or occlusion asdesired.

A third implementation of the second access disconnection system usespassive sonar. The blood stream in the extracorporeal circuit issubjected to a series of operations that introduce acoustic waves intoit. Blood pump, drip chamber, interaction with the dialyzer and thepatient each create an acoustic pattern. This sound pattern constitutesan acoustic signature, e.g., in the venous line when the needle islodged, will be different from the one when it is dislodged. The passivesonar implementation uses an acoustic transducer coupled to the venousline, which acts as a receiver. The receiver transducer monitors,processes and analyzes acoustic signals in the blood to create abaseline acoustic signature. When the pattern changes due to a venousneedle dislodgement, the processing of the received signal detects thischange and generates an alarm, etc.

A third access disconnection/ blood leak detection system uses opticalsensors. It is not uncommon that a small blood leak is present aroundthe areas at which the access needles connect to the patient's arm. Thiseffect, however, should be limited to a small area around the accesspoints. If the blood leak extends to a larger area, it likely indicatesneedle partial or full dislodgement, which must be addressedimmediately.

The optical system in one embodiment uses a flexible circuit havingdistributed optically reflective sensors. Here, flexible circuit wrapsaround the arm of the patient in one embodiment. In anotherimplementation, the optical system incorporates either a rigid orsemi-rigid circuit mounted on a flexible arm band made of plastic,rubber or cloth, for example. The arm band can also be disposable. Inany case, the attachment mechanism can be sized and configured to beattached alternatively for blood access with another body area, such asa patient's leg, or for catheter access, e.g., in the patient's neck.

The flexible circuit can be in contact with a piece of gauze coveringthe needle recess. For sterility the contact surface is cleaned with adisinfectant. Alternatively, the contact area is covered with a steriledisposable transparent film, which can be self-adhesive. The film isdiscarded after the treatment is completed.

The flexible circuit can be attached to the patient using a hook andloop type of mechanism, magnetic straps, magnetic buckle or other typeof releasably securable and cleanable apparatus.

The reflective optical sensors in one embodiment use of a light emittingdiode, such as a light source, and a photocell or phototransistor, asreceiver. The emitted light has a wavelength that has is chosen so thatthe color of blood absorbs its energy. As long as the light illuminatesa white gauze, a percentage of the light's energy is reflected towardsthe receiver. On the other hand, if blood on the gauze absorbs most ofall of light energy, the receiver detects a considerable loss of signaland signals or alarm, etc.

A local micro-controller in one embodiment gathers data from the opticalsensors and reports this data via, e.g., a radio frequency link, to thedialysis instrument. In one implementation, the micro-controller remainsin a sleep mode or power-save mode, which turns the optical sensors offuntil the dialysis instrument requests data via the radio frequencylink. The micro-controller then “wakes up”, energizes the light sources,reads the optical receivers and transmits the status back to thedialysis instrument. If one (or perhaps more than one) of the sensorsdoes not receive enough light, the processor issues a distress call and,additionally or alternatively, energizes an audible alarm. The machinetakes any other appropriate action, such as shutting down a pump orclamping a line or valve.

In a fourth access disconnection embodiment, the dialysis system usesthe patient's cardiovascular electrical system to detect an accessdisconnection. Humans have an internal electrical system that controlsthe timing of heartbeats by regulating: heart rate and heart rhythm.Generally, the body's electrical system maintains a steady heart rate ofsixty to one hundred beats per minute at rest. The heart's electricalsystem also increases this rate to meet the body's needs during physicalactivity and lowers it during sleep.

In particular, the heart's electrical system controls the timing of thebody's heartbeat by sending an electrical signal through cells in theheart, namely, conducting cells that carry the heart's electrical signaland muscle cells that enable the heart's chambers to contract. Thegenerated electrical signal travels through a network of conducting cellpathways by means of a reaction that allows each cell to activate theone next to it, passing along the electrical signal in an orderlymanner. As cell after cell rapidly transmits the electrical charge, theentire heart contracts in one coordinated motion, creating a heartbeat.

The system of the present disclosure uses an electrocardiogram orelectrogram (“ECG”) setup. In one implementation, a first electrode isattached to the venous line and a second electrode is attached to thepatient. The electrodes are connected electrically to signalconditioning circuitry. The signal conditioning circuitry produces ECGsignals when the arterial and venous connections are made properly. Whena partial or complete access disconnection occurs with either thearterial or venous needles, electrical communication with the body'selectrical system through the extracorporeal path is lost as is the ECGsignal. Additional circuitry detects this dropout and sends an accessdisconnection signal to the blood treatment machine.

Alternative ECG embodiments include the attachment of both first andsecond electrodes to the extracorporeal circuit. Also, blood access canbe made at or close to the patient's heart, increasing sensitivity tothe ECG signals, as opposed to access at the patient's arm. To that end,disclosed herein is an embodiment for a dialysis needle equipped withthe electrodes used for accessing the patient's blood at or near theheart. Also disclosed herein are various embodiments for tubing havingelectrodes implanted either inside the tubing, within the tubing oroutside the tubing. Depending on the electrode configuration, theelectrodes communicate electrically with the blood directly,capacitively, inductively, or wirelessly, e.g., through radio frequency.

The ECG system is also adaptable for other uses besides the detection ofvascular access disconnection. The ECG signals may be further processedto calculate other physiological parameters such as heart ratevariability, respiration, stroke volume, cardiac output and centralblood volume. To this end, an electrical source can be added to the ECGsystem to measure bioimpedance. Further, a solution can be injected intothe patient's body to assist in one or more of the above parameters. TheECG system can also be used to assist control of patients with heartrhythm management devices (pacemakers) via cardiac electrophysiologymeasurements to change cardiovascular parameters beneficially duringdialysis.

In a fifth system, a blood leak device using capacitive sensors isprovided. The device includes outer layers of insulation, e.g., plasticlayers. Inside, the device includes an array of capacitors. A layer ofshielding is also provided inside the shielding. If a blood leakdevelops beneath the capacitive device, the region of capacitors sensinga dielectric change grows. If the region stops growing, a system usingthe capacitive device assumes a normal amount of seepage has occurred,which is distinguishable from a blood leak or needle dislodgement. Ifthe blood leak grows large enough, the system using the capacitivedevice assumes that a partial or full access disconnection has occurredand causes an alarm.

In any of the above described access disconnection embodiments, thecircuitry for the access disconnection systems can be located locally atthe patient or sensing site, remotely within the machine, or somecombination thereof. Depending on the location of the circuitry, thesignal sent from the access disconnection system to the dialysis machinecan be a steady, e.g., conditioned digital signal, an intermittentsignal, a signal sent on command or some combination thereof. The signalcan be sent via wires or wirelessly.

Further, any of the above described access disconnection/blood leakdetection embodiments can be used alternatively in a redundant systemwith another, different type of access disconnection/blood leak system.For example, any system that looks for an electrical connection to bebroken (described loosely as an access disconnection system for ease ofdescription but in know way intending to limit the meaning of the term)can be combined with a system that looks for an electrical connection tobe made (described loosely as a blood leak detection system for ease ofdescription but in know way intending to limit the meaning of the term)to capitalize on benefits inherent with each type of system.

It is therefore an advantage of the present disclosure to provide animproved access disconnection system for blood treatment machines.

It is another advantage of the present disclosure to providenon-invasive access disconnection systems.

It is a further advantage of the present disclosure to provide accessdisconnection systems that do not induce current into the patient'sblood.

It is still another advantage of the present disclosure to provideaccess disconnection systems that do not add to disposable cost ormanufacture.

It is still a further advantage of the present disclosure to provideaccess disconnection systems that circumvent problems from to electricalreconnection due to lost blood.

It is yet another advantage of the present disclosure to provide anaccess disconnection system that yields other valuable blood parameterinformation.

It is yet a further advantage of the present disclosure to provideaccess disconnection systems that are compatible with blood needle andcatheter applications.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a known arterial and venous access configuration.

FIG. 2 is a sectioned elevation view showing one embodiment of an accessdisconnection system using ultrasound.

FIG. 3 is a perspective view showing the system of FIG. 2 and oneembodiment for it to communicate with a blood treatment machine.

FIG. 4 is a schematic view of one embodiment of the electronicsassociated with the system of FIG. 2.

FIG. 5 is a schematic view of one simulation of the ultrasound accessdisconnection system of FIG. 2.

FIG. 6 is a chart illustrating results from testing done on thesimulation of FIG. 5.

FIG. 7 is a perspective view showing one embodiment of an acousticaccess disconnection system, which employs two acoustic transducers.

FIG. 8 is a perspective view showing an additional embodiment of anacoustic access disconnection system, which employs active sonar, andwhich is system is depicted in a transmit phase.

FIG. 9 is a perspective view showing either (i) a receive phase of theactive sonar system of FIG. 8 or (ii) an alternative embodimentemploying a passive sonar system, wherein both systems “listen” toeither (i) an echo of the active transmitted signal or (ii) the acousticsignature of the extracorporeal circuit in the passive system.

FIG. 10 is a perspective view showing one embodiment of an opticalaccess disconnection system.

FIG. 11 is a perspective view showing one embodiment of a flexiblecircuit used with the optical access disconnection system of FIG. 10.

FIG. 12 is a schematic elevation view representing the optical accessdisconnection system of FIG. 10 in a normal state.

FIG. 13 is a schematic elevation view representing the optical accessdisconnection system of FIG. 10 in an access disconnection state.

FIG. 14 is a perspective view showing the optical system of FIG. 10 andone embodiment for it to communicate with a blood treatment machine.

FIG. 15 is a schematic view of one embodiment of a system that useselectrocardiogram (“ECG”) signals to detect an access disconnection.

FIG. 16 is a schematic view of another embodiment of a system that useselectrocardiogram (“ECG”) signals to detect an access disconnection.

FIG. 17 is a plan view of one embodiment for a cardiac catheter usedwith the ECG system of FIG. 16.

FIGS. 18A to 18C illustrate various embodiments for coupling anelectrical contact with the patient's blood, the embodiments capable ofbeing used with the systems of FIGS. 16 and 17.

FIGS. 19A and 19B are top and side views of a capacitive sensing bloodleak detection device.

DETAILED DESCRIPTION

The examples described herein are applicable to any medical fluidtherapy system requiring vascular access. The examples are particularlywell suited for the control of kidney failure therapies, such as allforms of hemodialysis (“HD)”), hemofiltration (“HF”), hemodiafiltration(“HDF”) and continuous renal replacement therapies (“CRRT”) requiringvascular access.

Ultrasound Remote Access Disconnection Sensor

Referring now to the drawings and in particular to FIGS. 2 to 4, anultrasound access disconnection system 10 is illustrated. FIG. 2 showsthe details of system 10. FIG. 3 shows one apparatus for attachingsystem 10 to patient 12. FIG. 3 also shows one embodiment forinterfacing system 10 with blood treatment or dialysis machine 100.While system 10 refers generally to the remote apparatus connected tothe patient as seen in FIG. 2, system 10 and indeed each of the systemsdescribed herein also includes the machine or instrument, such as adialysis machine. FIG. 4 shows an embodiment of the electronics (eitheronboard or remote electronics) associated with system 10. FIGS. 5 and 6provide test results.

Any of the vascular disconnection examples described herein, includingsystem 10, is operable with machine 100, which can include a diffusionmembrane or filter, such as a dialyzer, e.g., for HD or HDF, or ahemofiliter, e.g., for HF. Moreover, machine 100 and any of the accessdisconnection systems described herein may be used in clinical or homesettings. For example, machine 100 and the access disconnection systemsmay be employed in an in-center HD machine, which runs virtuallycontinuously throughout the day. Alternatively, they may be used in ahome HD machine, which can for example be run at night while the patientis sleeping.

Machine 100 in one embodiment has a dialysate (infusate) supply.Alternatively, multiple bags of dialysate supply are ganged together andused one after another. In such a case, the emptied supply bags canserve as drain or spent fluid bags. Further alternatively, machine 100can be used with an on-line source, such as one or more concentrate pumpconfigured to combine one or more concentrate with water to formdialysate on-line. On-line sources are used commonly with HD systems forexample.

Although not illustrated, machine 100 can operate with an in-line orbatch heater that heats the dialysate or infusate to a desiredtemperature. The heater can be located upstream or downstream of a freshsupply pump for example. Machine 100 includes a dialysate air trap,which can be located at or near the heater to capture air egression fromthe dialysate due to heating. Likewise, the extracorporeal circuitoperable with blood pump 102 also includes one or more air detector andair removal apparatus (e.g., air trap).

HD, HF, HDF or CRRT machine 100 also includes blood pumping systems,shown below, which are known generally in the art, e.g., the use of oneor more peristaltic blood pump. HD, HF, HDF or CRRT machine 100 alsoincludes dialysate proportioning systems, mentioned above, which arealso known and need not be described here. The '534 Patent, incorporatedherein by reference, describes a proportioning system for example.

Machine 100 also includes an apparatus and method for knowing how muchdialysate has been used for clearance and how much ultrafiltrationvolume has been removed. This apparatus controls and knows how muchultrafiltrate has been removed from the patient and controls theflowrate of dialysate to and from the dialyzer, extracorporeal circuitand/or hemofilter. The apparatus also ensures that the necessary amountof ultrafiltrate is removed from the patient by the end of treatment.

Machine 100 includes an enclosure 104 as seen in FIG. 3. Enclosure 104varies depending on the type of treatment, whether the treatment isin-center or a home treatment, and whether the dialysate/infusate supplyis a batch-type (e.g., bagged) or on-line. An in-center, on-lineenclosure 104 tends to be bigger and more robust due to the additionaldialysate producing equipment and the frequency of use of such machines.A home therapy enclosure 104 is desirably smaller and built so thatmachine 100 can be moved about one's home or for travel.

FIG. 2 illustrates that system 10 includes a transducer 24. Transducer24 in the illustrated embodiment includes a housing 26, which houses apiezoelectric crystal 28. Transducer 24 transmits power from one type ofsystem to another. In the piezoelectric embodiment, transducer 24 poweris provided in the form of electricity from a piezoelectric materialacted upon. System 10 includes a transducer excitation apparatus 42 asseen in FIG. 4, which applies an electrical field to piezoelectriccrystal 28. Piezoelectric crystal 28 undergoes mechanical deformationdue to the electric field. In this manner, crystal 28 is induced toresonate (vibrate) at a certain frequency to produce ultrasonic waves.In an embodiment, the ultrasonic waves are produced in the Mega-Hertzfrequency range. A layer of gel couples the waves to the patient in oneembodiment. The ultrasound waves in the presence of human tissue travelthrough the tissue to a depth that depends on the power and frequency ofthe excitation.

Housing 26 of transducer 24 in the illustrated embodiment is positionedin parallel with the arm and tissue of patient 12. Crystal 28 on theother hand is placed at an angle, e.g., forty-five degrees, relative tothe arm and tissue of patient 12 to produce ultrasound waves 30 a havingdirectional components both aligned with and perpendicular to thedirection of blood flow.

Blood cells 32, e.g., red blood cells, within the blood stream serve asreflectors for the ultrasound waves, echoing waves 30 b back towards asecond piezoelectric crystal 34. It should be appreciated however thatfirst piezoelectric crystal 28 could perform both emitter and receiverfunctions, in which case second crystal 34 is not needed. In theillustrated embodiment, receiver crystal 34 is located in the samehousing 26 of the same transducer 24 as is emitter crystal 28.Alternatively, receiver crystal 34 is located in a separate transducerhousing. In the illustrated embodiment, receiver crystal 34 is alsomounted at an angle, e.g., forty-five degrees, relative to the arm andtissue of patient 12.

For receiver piezoelectric crystal 34, reflected waves 30 b applymechanical stress to receiver crystal 34, causing crystal 34 to becomeelectrically charged and to vibrate at its resonant frequency creatingan ultrasound wave. The reflected ultrasound waves 30 b have a differentfrequency than do the emitted ultrasound waves 30 a, an effect known asthe Doppler effect. The change in frequency is dependent on the speedand direction of movement of blood cells 32 flowing though the accesssite. The electronics in system 10 stores software that processes thereceived echoes 30 b to determine blood parameters, such as, bloodflowrate of the red blood cells, peak flowrate of the reflectors,changes in blood flowrate, e.g., pulsatile characteristics of the bloodflow, turbulence in the access line as described in more detail below.

In the embodiment illustrated in FIG. 3, transducer 24 and theelectronics described below are held in place via bands 36. Bands 36have suitable fasteners, such as Velcro™ fasteners or other type offrictionally engaging fastener, buttoned or snap-fitted fastener. Bands36 serve a second function, namely, FIG. 2 shows that band 36 holdstransducer 24 against patient 12 via a gel 38. Gel 38 couples theultrasound wave into the patient's tissue.

FIG. 4 shows an embodiment of the electronics associated with system 10.A digital signal processor (“DSP”) 44, which can include onboard randomaccess memory (“RAM”) and read only memory (“ROM”), sends an outputsignal to transducer excitation appratus 42. Excitation apparatus 42excites emitter crystal 28 of transducer 24 as described above.Reflected waves 30 b cause receiver crystal 34 (or crystal 28 operatingas both emitter and receiver) to vibrate and create an ultrasound wave,which is sent to signal conditioning 40. Signal conditioning 40 in oneembodiment includes an analog to digital (“A/D”) converter, whichdigitizes the reflected wave into a form that DSP 44 can process. Signalconditioning 40 may, in another embodiment, contain demodulationcircuitry to separate the signal components in a manner useful forDoppler calculations, for example.

DSP using onboard software in one embodiment detects a flow or accesscondition, a no-flow or full-access disconnection condition or apartial-flow or partial access diconnection condition. DSP 44 also usesthe conditioned signals to detect blood flowrate, e.g., by equating aparticular frequency to a particular blood flowrate. The correlation canbe determined empirically and checked for repeatability. A peakfrequency corresponds to peak blood flowrate. DSP 44 also detectschanges in blood flowrate even when they do not rise to the levelindicating an access disconnection. This information can be used todetermine blood flow turbulence for example, which in turn can be usedfor example diagnostically to monitor or determine therapy efficiency oreffectiveness.

DSP 44 communicates back and forth with a remote or wirelessemitter/receiver 46, such as a radio frequency (“RF”) emitter/receiver.Other remote signals may be used alternatively, such as a microwavesignal. Further alternatively, system 10 is hard-wired to machine 100and communicates via electrical signals, e.g., 4 to 20 mA or 0 to 5 VDCsignals.

Machine 100 includes a wireless transmitter/receiver 48, such as an RFtransceiver. In system 10, communicator 48 instrument 100 sends messagesto and receives messages from the remote unit via communicator 46.Communicator 48 in turn communicates back and forth with a centralprocessing unit (“CPU”) 50 located within 100. CPU 50 in an embodimentincludes a supervisory processor that communicates via signals 56 withone or more delegate processor and circuit board or controller locatedwithin machine 100. Transducer 24, signal conditioning 40, excitationapparatus 42, DSP 44 and emitter 46 are located on a printed circuitboard (“PCB”) 52 in the illustrated embodiment. PCB 52 can be locatedwithin transducer housing 26, within a separate housing (notillustrated), or within a housing that also houses one or moretransducer 24. In an alternative embodiment, DSP 44 and its associatedfunctionality are located and performed, respectively, at CPU 50 ofmachine 100.

PCB 52 also includes a battery, a power supply or a combination of both,referred to generally herein as power supply 54. Supply 54 can be arechargeable battery, for example. Supply 54 powers the components ofPCB 52, such as, signal conditioning, DSP 44 and wireless communicator46. Power supply 54 is rechargeable in an embodiment and can be coupledto an audio, visual or audiovisual alarm that alerts the patient whenthe power supply needs to be recharged or replaced.

In the embodiment illustrated in FIG. 4, remote wireless communicator ortransceiver 46 communicates with instrument communicator 48 via an RFsignal 58. Signal 58 can be any of the following types: an electricalsignal, a radio frequency signal, a microwave signal, a continuoussignal, an intermittent signal, a signal sent only upon the sensing ofthe change and any suitable combination thereof. FIG. 3 shows that in anembodiment signal 58 is a continuous e.g., digitalized, data stream,which CPU 50 (via RAM 42 and DSP 44 and associated functions located inmachine 100) uses to determine blood flowrate, peak flowrate, pulsatilecharacteristics of the blood flow, turbulence and the like. If an accessdisconnection occurs, the frequency of reflected ultrasonic waves 30 bchanges significantly enough as does the output of corresponding signal58 that the software within buffering RAM 42 detects a partial or fullaccess disconnection. When the access disconnection is detected, CPU 50via signals 56 causes other components within machine 100 to takeappropriate action, e.g., causes an audio, visual or audiovisual alarmto appear on and/or be sounded from graphical user interface 106 ofmachine 100. CPU also likely causes blood pump 102 to shut down.

In an alternative embodiment, the processing of reflected waves 30 b isdone on PCB 52. Here, onboard DSP 44 determines blood flowrate, peakflowrate, pulsatile characteristics of the blood flow, turbulence andthe like. DSP 44 sends this information wirelessly via transceiver 46 toCPU 50 at predetermined intervals or when CPU 50 requests suchinformation. When an access disconnection is detected, DSP viatransceiver 46 sends an alarm signal 58 to CPU 50, which causes othercomponents within instrument 100 to take appropriate action as describedabove. Thus wireless signal 58 can be a continuous signal, anintermittent signal or a signal sent only upon the sensing of the changeand any suitable combination thereof.

In a further alternative embodiment, PCB 52 includes an audio, visual oraudiovisual alarm, which alarms a patient of an access disconnection. Inthis embodiment, system 10 may or may not communicate with machine 100.For example, PCB 52 can sound an alarm, while machine 100 shuts down oneore more pump and occludes or closes one or more line or valve.

FIG. 5 illustrates schematically a test that has been performed using anultrasound sensor, such as transducer 24 shown in FIG. 2, placed at theblood vessel of patient 12 downstream from venous needle 20 as also seenin FIG. 2. It should be appreciated that the systems described hereinare operable with standard access needles 16 and 20 or with subclaviantype catheters. As seen in FIG. 5, the patient's arm is modeled by atube. The ultrasound sensor is placed over the tube. The patient's bloodis modeled using saline, which an access pump pumps at approximately oneliter per minute through a five hundred cubic centimeter compliancechamber, through tube (modeling the patient ) and back into a source ofthe saline. Arterial and venous needles 16 and 20 shown schemtically inFIG. 5 are inserted or connected to the tube representing the patient'sarm. The simulated extracorporeal circuit includes a blood pump, dripchamber, in combination with a pressure sensor, dialyzer and venous sidepressure sensor.

FIG. 6 illustrates that when the venous access 20 was disloged from thetube, the ultrasound sensor noticed a discernable drop in flowrate ofabout 300 ml per minute. That is, the one liter per minute being pumpedby the access pump in FIG. 5 returned at only 700 ml per minute assensed by the ultrasound sensor.

Acoustic Access Disconnection Sensor

Referring now to FIGS. 7 to 9, various embodiments for acoustic accessdisconnection systems are illustrated by systems 60 a to 60 c (referredto herein collectively as acoustic access disconnection systems 60 orgenerally as acoustic access disconnection system 60). Accessdisconnection systems 60 have many similarities with ultrasound accessdisconnection system 10. Both are used with machine 100 (and each of itsalternative configurations discussed above), have remote signalingcapability, are non-invasive, do not circulate current through thepatient's blood, do not add components to the disposable cassette ortubing set, saving cost, and have additional blood parameter measurementcapability. Both systems 10 and 60 use sound waves.

One primary difference with systems 60 is that the transducers andassociated electronics are coupled to the arterial and venous lines 14and 18 instead of to patient 12. This configuration may be advantageousfrom the standpoint that a disconnection of one of the lines 14 and 18should produce a relatively dramatic change in reflected waves.Additional blood parameter measurements will reflect blood flowcharacteristics in the extracorporeal circuit rather than blood flowcharacteristics in the patient as with system 10, which may beadvantageous or disadvantageous.

Referring now to FIG. 7, a dual transducer transmit/receive acousticaccess system 60 a is illustrated. Acoustic access system 60 a includesa printed circuit board 66, which carries transducers 62 and 64, signalconditioning 40, excitation apparatus 42, DSP 44 (including onboardmemory) wireless transceiver 46 and power supply 54 described above.Power supply 54 as above powers excitation apparatus 42, DSP 44 andwireless transceiver 46, which operate as described above for system 10.DSP 44 communicates back and forth with remote transceiver 46, whichcommunicates back and forth with machine transceiver 48. In analternative embodiment, as with system 10 above, one or more of theapparatus and associated functionality of DSP 44 is located withinmachine 100. Machine 100 as before includes wireless, e.g., RFtransceiver 48 to send and to receive signals 58 to and from wirelesstransceiver 46. Alternatively, machine 100 is hardwired to system 60 afor electrical communication.

In the illustrated embodiment, acoustic emitter transducer 62 throughexcitation apparatus 42 transmits an acoustical signal into arterialline 14, while receiver transducer 64 receives an acoustical signal fromvenous line 18. Alternatively, emitter transducer 62 transmits anacoustical signal into venous line 18, while receiver transducer 64receives an acoustical signal from arterial line 14. Tranducers 62 and64 can be of a type in which each is constructed to be one of an emitteror a receiver. Alternatively, tranducers 62 and 64 are each bothtransmitters and receivers. Here, the roles of tranducers 62 and 64 uponan access disconnection event can be reversed to provide a redundantcheck. The roles of tranducers 62 and 64 can also be switched undernormal operation to test that the transducers are working properly andalso to provide redundancy for other parameters for which system 60 adetects.

In an embodiment, tranducers 62 and 64 transmit and receive waves thatare sonic, subsonic or pressure waves, for example, the signal can besent in a single or in multiple frequencies. Transducer 62 can emitwaves in a continuous, intermittent or pulsed manner. Further, theemitted signal can be modulated in any one or more combination ofamplitude, frequency or phase. In a preferred embodiment, the signal isdistinct from naturally occurring waves that receiver transducer 64 mayalso detect.

Excitation apparatus 42 excites acoustic emitter transducer 62 to emitsound waves in a direction towards patient 12. Acoustic receivertransducer 64 is likewise configured to receive sound waves from thepatient. In this manner, the likelihood that sound waves will travelfrom emitter transducer 62, around blood pump 102, to receivertransducer 64 is minimized. Further, a drip chamber located in one orboth of the arterial or venous lines provides an air barrier disconnectwithin the extracorporeal circuit, which should minimize sound wavecoupling towards the blood pump. This directional configuration alsomaximizes the difference in signal reception when an accessdisconnection.

Signal conditioning 40 (e.g., an A/D converter) conditions the signalfor DSP 44. It should be appreciated that the signal conditioning can belocated alternatively within DSP 44. DSP 44 processes the conditionedsignals using an onboard or a separate buffering RAM. DSP communicateswith transceiver 46, which in turn sends and receives data frominstrument transceiver 48. Transceiver 46 can alternatively be locatedonboard DSP 44. In any case, DSP 44 can be configured to detect adislodgement by measuring a loss in power of the acoustic signal duringdisconnection. DSP 44 could also calculate blood flowrate, peak flowrateand any of the other parameters discussed herein.

If either arterial line 14 or venous line 18 becomes partially orcompletely disloged from patient 12, communication between tranducers 62and 64 is broken or altered significantly enough that an accessdisconnection determination is made and any of the protective actionsdiscussed herein, e.g., alarm, pump shutdown, valve closing, lineoccluding is carried out. In the illustrated embodiment, the processingof the breaking or interruption of communication between tranducers 62and 64 is done on PCB 66. Here, under normal operation, PCB 66determines the power and frequency of the received signal, andpotentially, blood flowrate, peak flowrate, pulsatile characteristics ofthe blood flow, turbulence and the like as described above. Thisinformation is sent wirelessly via transceiver 46 to CPU 50 ofinstrument 100 on a continuous basis, at predetermined intervals, orwhen CPU 50 requests such information. When an access disconnection isdetected, DSP via emitter 46 sends an alarm signal 58 to CPU 50, whichcauses other components within machine 100 to take appropriate action asdescribed above. The wireless signal 58 can accordingly be a continuoussignal, an intermittent signal, a signal sent only upon the sensing ofthe change and any suitable combination thereof.

In an alternative embodiment, the various components of PCB 66 areprovided in machine 100 such as DSP 44. Here, the RF signal 58 is acontinuous data stream, which can be conditioned e.g., digitized,locally and sent to CPU 50 of machine 100. DSP 44 now within instrument100 uses data stream 58 to determine the power and frequency of thereceived signal, and potentially, blood flowrate, peak flowrate,pulsatile characteristics of the blood flow, turbulence and the likewithin machine 100. If an access disconnection occurs, the datacontained in the RF signal 58 changes enough so that the software withininstrument 100 detects a partial or full access disconnection. When theaccess disconnection is detected, CPU 50 causes, e.g., through adelegate controller, other components within machine 100 to takeappropriate protective action as described above.

In a further alternative embodiment, PCB 66 includes an audio, visual oraudiovisual alarm, which alarms a patient of an access disconnection. Inthis embodiment, system 10 may or may not communicate with machine 100.

Referring now to FIGS. 8 and 9, an active sonar or echo system 60 bemploys either a single acoustic transducer 68, doubling as transmitterand receiver (as illustrated), or dual transducers, one emitting and onereceiving. In either case, the single or dual transducers are coupled toa single one of the extracorporeal lines, e.g., venous line 18 in onepreferred embodiment (as described above venous access dislodgment ispotentially more dangerous than arterial access dislodgement).

Active sonar or echo system 60 b includes a printed circuit board 70,which carries signal conditioning 40, excitation apparatus 42, DSP 44,wireless remote transceiver 46 and power supply 54 described above.Power supply 54 powers signal conditioning 40, DSP 44 and transceiver46. In an alternative embodiment, as with system 10 above, one DSP 44 islocated within machine 100. Machine 100 as before inlcudes wireless,e.g., RF, transceiver 48 to receive signals from RF emitter 46.Alternatively, machine 100 is hardwired to system 60 b for electricalcommunication.

In the illustrated embodiment, acoustic emitter transducer 68 transmitsan acoustical signal into the blood of venous line 18. The signalreflects in the extracorporeal circuit lines 14, 18 and graft 22,producing a signature response. Signal conditioning 40 processes thesignature response, e.g., digitizes it, and sends a digital signal toDSP 44 (which can include RAM, ROM, onboard signal conditioning and/oronboard transceiver) located either locally at PCB 70 or at machine 100.DSP 44 analyzes the signal using onboard software in one embodiment. DSP44 formulates a baseline acoustic signature of the reflected acousticalwave and stores such baseline signal in RAM 42.

Acoustic emitter/receiver transducer 68 is configured to emit soundwaves in a direction towards patient 12. Transducer 68 is likewiseconfigured to receive sound waves from the patient. The likelihood thatsound waves will travel from transducer 68, around blood pump 102, backto transducer 68 is minimal due at least in part to a drip chamber thatis located between the transducer and the blood pump in the arterialblood line. This directional configuration also maximizes the differencein signal reception when an access disconnection occurs.

If either arterial line 14 or venous line 18 becomes partially orcompletely disloged from patient 12, the signature response back totransducer 68 is broken or altered significantly enough compared to thebaseline acoustic signature, that an access disconnection determinationis made and any of the actions discussed herein is performed, e.g.,alarm, pump shutdown, valve closing, line occluding.

In the illustrated embodiment, the processing of the difference betweenthe received response and the baseline response is done at PCB 70. Here,under normal operation, onboard DSP 44 determines the power, frequencyand shape of the envelope of the received signal, and potentially, bloodflowrate, peak flowrate, pulsatile characteristics of the blood flow,turbulence and the like. This information is sent wirelessly via DSP 44and communicator 46 to CPU 50 continuously, at predetermined intervals,or when CPU 50 requests such information. When an access disconnectionis detected, DSP 44 via communicator 46 sends an alarm signal to CPU 50,which causes other components within machine 100 to take appropriateaction as described above. The wireless signal can accordingly be acontinuous signal, an intermittent signal, a signal sent only upon thesensing of the change and any suitable combination thereof.

In an alternative embodiment, the majority of the components of PCB 70are provided in machine 100. Here, the RF signal 58 is a continuous datastream, which can be conditioned, e.g., digitized, locally and sent tothe CPU of machine 100, which operates with DSP 44 and their associatedfunctions. Data stream 58 is used to determine blood flowrate, peakflowrate, pulsatile characteristics of the blood flow, turbulence andthe like within machine 100. If an access disconnection occurs, the RFsignal 58 is interrupted or is otherwise reduced enough that thesoftware within buffering DSP 44 detects a partial or full accessdisconnection. When the access disconnection is detected, CPU 50 causesother components within machine 100 to take appropriate action asdescribed herein.

In a further alternative embodiment, PCB 70 includes an audio, visual oraudiovisual alarm, which alarms a patient of an access disconnection. Inthis embodiment, system 10 may or may not communicate with machine 100.

Referring again to FIG. 9, a passive sonar or acoustic signature system60 c employs a single receiver transducer 64. Transducer 64 is coupledto a single one of the extracorporeal lines, e.g., venous line 18 in onepreferred embodiment (as described above venous access dislodgment ispotentially more dangerous than an arterial access dislodgement).

Passive sonar or acoustic signature system 60 c includes printed circuitboard 70, which carries signal conditioning 40, excitation apparatus 42,DSP 44, wireless communicator 46 and power supply 54 described above. Inan alternative embodiment, as with the systems above, one or more of theapparatuses and associated functionality of DSP 44 is located withinmachine 100.

Passive sonar system 60 c uses pulses generated by the system's bloodpump, drip chamber, interaction with the dialyzer or otherextracorporeal device. These devices create an acoustical pattern orsignature response at receiver transducer 64, similar to the signatureresponse discussed above. Signal conditioning 40 processes the signatureresponse, e.g., digitalizes it, and sends a digital signal to DSP 44,located either locally at PCB 70 or at machine 100. DSP 44 analyzes thesignal using onboard software in one embodiment. DSP 44 formulates abaseline acoustic signature of the reflected acoustical wave and storessuch baseline signal in memory.

If in the illustrated embodiment, venous line 18 becomes partially orcompletely disloged from patient 12, the signature response back totransducer 68 is broken or altered significantly enough compared to thebaseline acoustic signature, that an access disconnection determinationis made. Any of the actions discussed herein is then performed, e.g.,alarm, pump shutdown, valve closing, line occluding is carried out.

In the illustrated embodiment, the processing of the difference betweenthe received response and the baseline response is done on PCB 70 ofsystem 60 c. Here again, under normal operation, onboard DSP 44determines blood flowrate, peak flowrate, pulsatile characteristics ofthe blood flow, turbulence and the like. This information is sentwirelessly via DSP 44 and transceiver 46 to CPU 50 continuously, atpredetermined intervals, or when CPU 50 requests such information. Whenan access disconnection is detected, DSP via transceiver 46 sends analarm signal to CPU 50, which causes other components within machine 100to take appropriate action as described herein.

In an alternative embodiment, DSP 44 is provided in machine 100. Here,the RF signal 58 is a continuous data stream, which can be conditioned,e.g., digitized, locally and sent to the CPU of machine 100 via RFcommunication. Again, data stream 58 can be used to determine bloodflowrate, peak flowrate, pulsatile characteristics of the blood flow,turbulence and the like within machine 100. If an access disconnectionoccurs, the RF signal 58 is interrupted or is otherwise reduced enoughthat the software within buffering DSP 44 detects a partial or fullaccess disconnection. When an access disconnection is detected, CPU 50causes, e.g., via a delegate controller, other components within machine100 to take appropriate protective action as described above.

In a further alternative embodiment, PCB 70 of system 60 c includes anaudio, visual or audiovisual alarm, which alarms a patient of an accessdisconnection. In this embodiment, system 10 may or may not communicatewith machine 100.

Optical Access Disconnection/Blood Leak Detector

Referring now to FIGS. 10 to 14, an embodiment of an optical accessdisconnection/blood leak detection system 80 is illustrated. Opticalaccess disconnection/blood leak detection system 80 takes advantage ofthe gauze that is normally applied to patient 12 over access needles 16and 20. It is not uncommon that under normal operation a small leak ispresent around the access points in which needles 16 and 20 connect topatient's arm 12. The normal blood leakage however should be limited toa small area around access needles 16 and 20. If the blood leak extendsto a larger area, it likely indicates a needle dislodgement that needsto be addressed immediately.

FIG. 10 illustrates that optical access disconnection/blood leakdetection system 80 provides a flexible circuit 90. Flexible circuit 90wraps around arm 12 of the patient. In an embodiment, flexible circuit90 is placed over the gauze pad 82 shown in FIG. 10, which as mentionedis placed over access needles 16 and 20. Because the flex circuit 90contacts gauze 82, sterility needs to be considered. In one embodiment,flexible circuit 90 is cleaned with a disinfectant prior to being placedover gauze 82. In an alternative embodiment, gauze 82 is covered with asterile disposable film 84, which can be self-adhesive. Here, film 84 isdiscarded after treatment is completed. Film 84, isolates flexiblecircuit 90 from the contact area.

Arm band system 90 provides preventive action against needledislodgement. By wrapping around the needles and tubing, flexiblecircuit 90 secures the needles and tubing in position and accordinglytends to prevent dislodgement. Arm band system 90 confines theconnections between the fistulas and associated tubing to an areacovered by flexible circuit 90, so that the system can also detect adisconnection between the fistula and the tubing.

FIG. 11 illustrates that flexible circuit 90 in one embodiment includeshooks 86 a to 86 c, which loop around flex circuit 90 and attach, e.g.,frictionally and/or adhesively, to mating pads 88 a to 88 c,respectively. For example, hooks 86 (referring collectively to hooks 86a to 86 c) can attach to pads 88 (referring collectively to pads 88 a to88 c) via a Velcro™ type attachment, buttons, slits, folds or othertypes of releasably securable mechanisms. If it is found that hooks 86and pads 88 are difficult to clean, they can be replaced in oneembodiment with a more hygienic attach mechanism, such as magneticstraps and buckles.

As seen in FIGS. 10 and 11, flexible circuit 90 includes a plurality ofreflective photo sensors 92 a to 92 e, which are each powered via leads94 a to 94 e, respectively, connecting to a power source 54, such as acoin battery. Optical sensors 92 (referring collectively to sensors 92 ato 92 e) in an embodiment include a light emitting diode (“LED”) actingas the light source, and a photocell or phototransistor, acting as alight receiver. The LED and photosensor are configured for a specificwavelength that allows maximum absorption when reflected in blood.LED/Photosensor combinations such as ones used in hemodialysis bloodleak detectors have been used successfully in a prototype of opticalsystem 80.

Leads 94 (referring collectively to leads 94 a to 94 d) in an embodimentare trace, e.g., copper traces, that are applied in a known process toflexible circuit 90. In an embodiment, flexible circuit 90 uses anelectrically insulative material, such as a polyamide or Kapton™ film96. Film 96 in an embodiment is provided in multiple plies, with leads94 and photosensors 92 sandwiched between the multiple pliers 96.

Power supply 54 in an embodiment is also sandwiched between the multipledielectric films 96. Power supply 54 in one embodiment also powers amicrocontroller 98, which can include any one or more of signalconditioning 40, RAM 52, DSP 44 and RF emitter 46 described previouslyherein. Microcontroller 98 can also include an audible alarm and/or avideo status indicator, such as an LED, which signals whetherelectronics of optical access disconnection/blood leak detection system80 are performing properly.

FIGS. 12 and 13 illustrate one embodiment for operating photoelectricsystem 80. In an embodiment, light emitted from the LED of photosensor92 has a wave length for example in the range of the blue to green ofthe ultraviolet wave spectrum, which is absorbed by the color of bloodcollected on gauze 82. When light from sensor 92 illuminatesnon-bloodied or white gauze 82 shown in FIG. 12, a percentage of itsenergy reflects towards a receiver, e.g., photocell or phototransistor,of photosensor 92. In FIG. 13 on the other hand, the presence of bloodon gauze 82 absorbs most of all light energy emitted from sensor 92,such that sensor 92 receives and detects considerably less light, e.g.,a loss of signal. Accordingly, in FIG. 13 the arrow from gauze 82 backto photosensor 92 indicating reflected light is not shown.

In the embodiment illustrated in FIG. 11, sensors 92 a to 92 e arespaced a relatively far distance from access needles 16 and 20, e.g., onthe order of one inch to three inches from the needles, such that ifblood reaches sensors 92, it has traveled a distance sufficient from theaccess points to signal an access disconnection rather than a normalamount of blood leakage. Further, using multiple sensors 92 a to 92 eallows redundancy to be built into the software, in which for examplethe software looks for multiple ones of sensors 92 to show a lack ofreflection before determining that an access disconnection has occurred.Alternatively, a single sensor 92 sensing blood can be taken to indicatean access disconnection.

In one implementation, two or more concentric rings of optical sensorsof different diameters form a sensor array that allows the system tomonitor the progress of a blood leak. One of the sensors of the internalring (small diameter sensors) looks for a lack of reflection that, dueto the sensor's small diameter, is considered insignificant. If the nextring of (larger diameter) sensors does not lose reflected light, thesystem determines that the leak is not serious. Should the leak becomeserious, it reaches the outer ring of larger diameter sensors. Thesystem uses the time between detections in successive rings to determinethe flow of the blood leakage. The spacing between rings allowsestimation of the volume of blood leakage.

Microcontroller 98 gathers data from optical sensors 92 and reports thisdata in an embodiment via RF signal 58 to dialysis machine 100. Machine100 can include at least one of signal conditioning 40, DSP 44 (whichcan have onboard RAM and ROM as well as other apparatus andfunctionality as described herein), which are used to analyze signal 58.In an alternative embodiment, microcontroller 98 includes signalconditioning, such as an analog to digital converter and/or signalsumming circuitry, which can combine the outputs from each of thephotosensors 92 to yield a single digitized signal 58, which isrepresentative of entire flex circuit 90. In a further alternativeembodiment, the software and processing is stored in microcontroller 98,in which case signal 58 tells the machine 100 whether or not an accessdisconnection takes place. Again, signal 58 can be continuous,intermittent, sent only when commanded, etc.

To save the power of supply 54, microcontroller 98 in one embodiment ismaintained in a sleeve or power save mode and optical sensors 92 are offuntil dialysis instrument 100 requests data from the radio frequencylink. At this point, microcontroller 98 “wakes up”, energizes lightsensors 92, reads signals from optical receivers of sensors 92 andtransmits status information back to dialysis instrument 100. In oneembodiment, again, if any of sensors 92 a to 92 e does not receiveenough light, DSP 94 issues a distress call to machine 100 andsimultaneously energizes an audio alarm. Machine 100 can cause any othersuitable protective action described herein to be taken.

Electrocardiogram (“ECG”) Remote Access Disconnection Sensor

Referring now to FIGS. 15, 16, 17 and 18A to 18C, various systems areshown that detect an access disconnection using signals form anelectrocardiogram (“ECG”). Generally, an ECG is a test that measureselectrical signals that control the rhythm of a person's heartbeat. Theheart is a muscular pump made up of four chambers, two upper chamberscalled atria and two lower chambers are called ventricles. A naturalelectrical system causes the heart muscle to contract and pump bloodthrough the heart to the lungs and the rest of the body.

Electrodes for the ECG are placed on a patient's skin to detect thisnatural electrical activity of the heart. In system 120 of FIG. 15,during dialysis therapy, a first electrode 122 is attached to venousline 18, while a second electrode 124 is attached to the patient's skin,for example, at leg 12 a (as shown here), arm 12 b, or chest 12 c ofpatient 12 or is alternatively connected to arterial line 14. Electrodes122 and 124 can be connected at venous line 18 and arterial line 14through direct contact, capacitive coupling, inductive coupling,wireless or otherwise. Alternatively, multiple body electrodes 124 canbe placed at different locations 12 a, 12 b, 12 c of patient 12.

FIGS. 18A to 18C show three possible arrangements for contact/bloodcoupling. In FIG. 18A, electrode 122 is placed inside venous line 18 andcontacts blood directly. In FIG. 18B, electrode 122 is embedded withinthe wall of venous line 18 and couples to the blood, e.g., capacitivelyor inductively. In FIG. 18C, electrode 122 is placed outside of venousline 18 and likewise couples to the blood, e.g., capacitively orinductively. The electrodes can be metal or of a conductive polymermaterial.

System 120 of FIG. 15 shows a blood pump 102 and dialyzer 108 connectedto arterial line 14 and venous line 18. The extracorporeal circuitincludes other components not illustrated here for convenience. Also,dialyzer 108 communicates with a dialysate source, e.g., bagged oron-line, an pumps that deliver dialysate to the dialyzer 108, whichagain are not shown for convenience. The ′454 Patent referenced abovediscloses further details concerning the extracorporeal and dialysatecircuits, which are applicable to each of the systems described herein.The teachings of each of the systems described herein are alsoapplicable to access disconnection in hemofiltration andhemodiafiltration systems.

Electrodes 122 and 124 are connected electrically to signal conditioning40 and signal processing, which can include RAM 42 and DSP 44 as hasbeen discussed herein. Any of signal conditioning 40, RAM 42 and DSP 44can be located locally or remotely as desired and as discussed herein.

Electrodes 122 and 124 can alternatively or additionally be connected toa machine that translates the electrical activity into anelectrocardiogram, which may show: evidence of heart enlargement, signsof insufficient blood flow to the heart, signs of a new or previousinjury to the heart (e.g., due to a heart attack), heart rhythm problems(arrhythmias), changes in the electrical activity of the heart caused byan electrolyte imbalance in the body, and signs of inflammation of thesac surrounding the heart (pericarditis). These parameters may be usefulduring dialysis as discussed in more detail below.

Under normal conditions, the natural electrical signals that control therhythm of a person's heartbeat create a signal 126 shown figuratively inFIG. 15. Upon an access disconnection of venous line 18 in theillustrated embodiment, signal 126 is no longer sensed becauseelectrical communication with the body through the blood is lost.Machine 100 sees the lack of signal 126 as an access disconnection andcauses any of the measures discussed herein to be taken.

FIGS. 16 and 17 illustrate an alternative system 140 and catheterassembly 142 used in system 140, respectively. In system 140 of FIG. 16,a cardiac catheter access at chest 12 c of patient 12 using cardiaccatheter assembly 142 is used. Cardiac access and catheter assembly 142provide a more direct access to the heart and its associated signalsthan does needle access at the arm 126 of patient 12. Cardiac access andcatheter assembly 142 may be better suited for acute treatments. Here,the doctor can more directly monitor electrograms from the blood poolinside the heart and provide more or better information about thecardiac function than with typical arterial and venous access, whilestill dialyzing patient 12.

Catheter 146 of assembly 142 is equipped with electrodes, such aselectrodes 122 and 124, via any of the configurations shown inconnection with FIGS. 18A to 18C. Catheter assembly 142 includes anarterial access section 114 and a venous access section 118, whichconnect respectively to arterial line 14 and venous line 18 of theextracorporeal circuit. Catheter assembly 142 also includes a guide wire144 for directing catheter 146 to a desired location, e.g., directlyinto the patient's heart or to a desired local vein, artery or graft.

In systems 120 and 140, signal processing via DSP 44 additionally oralternatively processes signal 126 to calculate any one or more of heartrate variability, respiration, stroke volume, cardiac output and centralblood volume. Further, a bioimpedance source 130 is connected to thepatient, so that system 120 may make bioimpedance measurements.Additionally or alternatively, systems 120 and 140 allow for theinjection of a solution into the extracorporeal circuit, which is usedfor pacing control for patients having implanted cardiac rhythmmanagement devices (pacemakers). System 120 and 140 allow for keycardiovascular parameters to be monitored during dialysis, which mayhave beneficial effects on the dialysis therapy or be used for otherpurposes.

Bioimpedance in general is a measure of changes in the electricalconductivity of the thorax or heart. It can for example be a measurebased on pulsatile blood volume changes in the aorta. Bioimpedance isrelevant to the measurement of cardiac output and circulating bloodvolume.

In particular, thoracic electrical bioimpedance (also referred to asimpedance cardiography) has been investigated as a noninvasive way toassess cardiac output and other cardiovascular functions. Changes incardiac output are used to identify a change in the hemodynamic statusof a patient or to ascertain the need for, or response to, treatment,e.g., for critically ill patients and patients at high risk formorbidity and mortality.

Thoracic bioimpedance has been investigated for a variety ofindications, including, evaluation of the hemodynamics of patients withsuspected or known cardiovascular disease, differentiation ofcardiogenic from pulmonary causes of acute dyspnea, optimization ofatrioventricular interval for patients with A/V sequential pacemakers,and optimization of drug therapy in patients with congestive heartfailure.

Any of the above parameters may be monitored either in connection withdialysis or as an additional benefit of the treatment.

Capacitive Blood Leak Detection System

FIGS. 19A and 19B illustrate an alternative blood leak detection device150, which wraps around a patient's arm in any of the manners discussedabove with system 80 and covers access needles 16 and 20. Device 150includes an array of mini-capacitors 152 as seen best in FIG. 19A.Waterproof, e.g., plastic, insulators 154 a to 154 c are placed aroundboth sides of the capacitors. A ground or shield 156 is placed betweenthe backside of capacitors 152 and rear insulator 154 c.

Device 150 does not have to absorb blood to detect a blood leak. Thepresence of blood beneath mini-capacitors 152 results in a change in thedielectric field surrounding the capacitors. That is, if a wet spotdevelops beneath device 150, the region of capacitors 152 sensing adielectric change would grow. If the region stops growing, the systemusing device 150 (which can be any of the remote or wired systemsdiscussed herein) assumes a normal amount of seepage has occurred, whichis distinguishable from a blood leak or needle dislodgement. A smallamount of seepage is a common occurrence at “needle sticks” and shouldnot produce an alarm. If the blood leak grows large enough, the systemusing device 110 assumes that a partial or full access disconnection hasoccurred and sounds an alarm.

Redundant Access Disconnection/Blood Leak Detection System

Certain known access disconnection systems rely on the breaking of anelectrical circuit to detect an access problem. One problem with thesesystems is that a needle dislodging from the patient does not alwaysbreak the electrical circuit. A needle can for example dislodge from thepatient but direct the flow of blood over the access from which theneedle has been dislodged or over the other (e.g., arterial) needle tocomplete or re-complete the electrical circuit. Here, blood would not bereturned to the patient but no alarm would sound.

Other known systems assume that a dislodged needle will direct the flowof blood onto a part of the device or system. Here, if the needle isdislodged completely and quickly from under the device, the flow ofblood that is supposed to seep onto a part of the system may not (or notenough) and again no alarm is sounded.

To address the above described problems, any of the above-describedsystems can be used in combination with one another or in combinationwith other types of access disconnection or blood leak detectionsystems. In particular, a dislodgement type system can be combined witha blood leak detection system. Optical system 80 for example is a bloodleak detection system, which is particularly adept at detecting bloodleaking at the access site. Another type of blood leak detection systemis a conductive blanket or pad, which covers the access site in a mannersimilar to system 80 of FIGS. 10 to 14. The conductive blanket or padincludes contacts which form a closed electrical loop when contacted byblood seeping from the patient access. An additional blood leakdetection system 150 is disclosed above in connection with FIGS. 19A and19B.

Dislodgement systems, such as impedance sensing systems described in the'098 and '480 Patents discussed above, are particularly adept atdetecting when a needle or other access instrument has become fullydislodged from the patient. Ultrasound access disconnection system 10,acoustic systems 60 a to 60 c and bioimpedance system 120 are alsodislodgement type systems that adeptly detect a full needledislodgement.

Accordingly, it is contemplated to combine one of each of the blood leakdetection systems and needle dislodgement systems in a hybrid orredundant system, which adeptly detects either failure mode. Forexample, any one of the impedance systems of the '098 and '480 Patents,ultrasound access disconnection system 10, acoustic systems 60 a to 60 cand bioimpedance system 120 (fall dislodgement) can be combined with anyone of the optical (system 80), conductive blanket or capacitive (device150) blood leak detection systems, so that the manner in which thevenous needle has been dislodged does not matter. The accessdisconnection system causes an alarm if the venous needle is dislodgedquickly and falls off of the patient. The blood leak detection systemcauses an alarm if the venous needle is partially of fully dislodged anddirects blood flow over the venous or arterial needle.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. An access disconnection system comprising: a material capable of absorbing blood from a patient upon an arterial or venous line disconnection; a plurality of light emitters positioned to emit light onto the material; a plurality of light receivers positioned to receive light reflected off of the material, the light receivers being positioned in a first ring having a first diameter and a second ring having a second diameter, the first and second rings being concentric, and the first diameter being smaller than the second diameter; and electronic circuitry operably coupled to the plurality of light emitters and receivers, the circuitry configured to provide: (i) a first output when the light receivers of the first ring detect that the received light reaches or passes a particular level and light receivers of the second ring detect that the received light does not reach the particular level, and (ii) a second output when the light receivers of the first and second rings both detect that the received light reaches or passes the particular level, and wherein the light recevivers included within the first ring are positioned a d istance less than three inches (7.6 cm) from a portion of the material intended to cover the arterial line and venous line connections, such that the location that light is reflected off of the material provides for an allowable amount of blood seepage from the patient due to a needle stick.
 2. The access disconnection system of claim 1, which includes an attachment mechanism operable to attach the material to an arm of the patient.
 3. The access disconnection system of claim 1, wherein the light emitters emit light having a wavelength causing the light to be absorbed by blood.
 4. The access disconnection system of claim 1, which includes at least one of : (i) the material being gauze; (ii) the light emitters being a light emitting diode; and (iii) the light receivers being a photocell or phototransistor.
 5. The access disconnection system of claim 1, which includes a film positioned between the material and the light emitters/receivers, the material selected to allow light to pass through the material.
 6. The access disconnection system of claim 1, wherein the electronic circuitry is configured to provide the first and second outputs when light received by the receivers fall to the particular level.
 7. The access disconnection system of claim 1, wherein the particular level is an at least substantially no-light received level.
 8. The access disconnection system of claim 1, wherein the first and second outputs are of a type selected from the group consisting of: an electrical output and a radio frequency output.
 9. The access disconnection system of claim 1, which includes a blood treatment unit, the first and second outputs sent to the blood treatment unit.
 10. The access disconnection system of claim 9, wherein the blood treatment unit performs at least one of: (i) determines if the amount of light received warrants an access disconnection condition; (ii) alarms the patient upon receiving the second output; and (iii) shuts down at least one of a blood pump and a dialysate pump upon receiving the second output.
 11. The access disconnection system of claim 1, which includes a battery supply to at least one of the light emitters and light receivers.
 12. The access disconnection system of claim 1, which is a redundant system that combines one of: (i) an electrical impedance access disconnection detector, (ii) an ultrasound access disconnection detector, (iii) an acoustic access disconnection detector and (iv) a bioimpedance access disconnection detector with the light emitters, light receivers and electronic circuitry.
 13. An access disconnection system comprising: a material capable of absorbing blood from a patient upon an arterial or venous line disconnection; a plurality of light emitters positioned to emit light onto the material; a plurality of light receivers positioned to receive light reflected off of the material, the light receivers being positioned in a first ring having a first diameter and a second ring having a second diameter, the first and second rings being concentric, and the first diameter being smaller than the second diameter; and a flexible circuit including electronic circuitry operably coupled to at least one of the plurality of light emitters and light receivers, the circuitry configured to provide: (i) a first output when the light receivers of the first ring detect that the received light reaches or passes a particular level and light receivers of the second ring detect that the received light does not reach the particular level, and (ii) a second output when the light receivers of the first and second rings both detect that the received light reaches or passes the particular level, and wherein the plurality of light receivers included within the first ring are positioned peripherally along the flexible circuit, such that the location that light is reflected off of the material is a distance less than three inches (7.6 cm) from the arterial or venous line connection providing for an allowable amount of blood seepage from the patient due to a needle stick.
 14. The access disconnection system of claim 13, wherein the electronic circuitry is configured to provide the access disconnection second output when light received by the at least one receiver falls to the particular level.
 15. The access disconnection system of claim 13, which includes a blood treatment unit, the first and second outputs sent to the blood treatment unit.
 16. The access disconnection system of claim 15, wherein the blood treatment unit performs at least one of: (i) determines if the amount of light received warrants an access disconnection condition; (ii) alarms the patient upon receiving the second output; and (iii) shuts down at least one of a blood pump and a dialysate pump upon receiving the second output.
 17. The access disconnection system of claim 15, which is a redundant system that combines one of: (i) an electrical impedance access disconnection detector, (ii) an ultrasound access disconnection detector, (iii) an acoustic access disconnection detector and (iv) a bioimpedance access disconnection detector with the plurality of light emitters, plurality of light receivers and electronic circuitry.
 18. The access disconnection system of claim 13, wherein the circuitry is configured to measure a time between the start of the first output and the start of the second output.
 19. The access disconnection system of claim 12, wherein the plurality of light emitters are positioned in proximity to the plurality of light receivers in the first and second rings. 